Tracking the position of intrabody objects, such as sensors, tubes, catheters, dispensing devices, and implants, is required for many medical procedures. Systems have been developed that determine the position of an intrabody object by measuring voltage differentials between electrodes on an intrabody object and on the surface of the body. The voltage differentials correspond to the impedance between the electrodes. Methods for impedance-based position sensing are disclosed, for example, in U.S. Pat. No. 5,983,126 to Wittkampf and in U.S. Pat. No. 6,456,864 to Swanson, both of whose disclosures are incorporated herein by reference.
Wittkampf also describes a method for calibrating the position sensing apparatus using two electrodes spaced from each other on a catheter by a known distance. Measuring the voltages between each of the catheter electrodes and each of three body surface electrodes x, y, and z, permits a correlation between intrabody position and voltages in the x, y and z directions.
Similar methods for sensing voltage differentials between electrodes are disclosed by U.S. Pat. No. 5,899,860 to Pfeiffer; U.S. Pat. No. 6,095,150 to Panescu; and U.S. Pat. Nos. 6,050,267 and 5,944,022 to Nardella, all of whose disclosures are incorporated herein by reference.